Dynamic Wheel-Rail Force-Based Track-Irregularity Evaluation for Ballasted Track on Serviced Railway by Adjacent Excavation

This study investigates a load-based, track-irregularity-analysis technique for ballasted tracks on a serviced railway line with respect to excavation work conducted in adjacent sites. A numerical analysis and field measurements (railbed-settlement-monitoring sensor, track-geometry-measurement system, wheel-load measurements) were analyzed comparatively to demonstrate the correlation between the track irregularities and the Wheel-Rail interaction force. In this way, we highlight the necessity for load-based track-irregularity-management methods. The analyzed results show that the maximum dynamic wheel load was measured in the range of approximately 10 m before and after the location where the maximum track irregularities occurred, and that even if the maintenance criteria of track irregularities were satisfied, the design dynamic wheel load could still be exceeded depending on the train speed, thus indicating that track damage can be caused by the impact load.

Development of Condition Assessment Index of Ballast Track Using Ground-Penetrating Radar (GPR)

The condition of the ballast is a critical factor affecting the riding quality and the performance of a track. Fouled ballast can accelerate track irregularities, which results in frequent ballast maintenance requirements. Severe fouling of the ballast can lead to track instability, an uncomfortable ride and, in the worst case, a derailment. In this regard, maintenance engineers perform routine track inspections to assess current and future ballast conditions. GPR has been used to assess the thickness and fouling levels of ballast. However, there are no potent procedures or specifications with which to determine the level of fouling. This research aims to develop a GPR analysis method capable of evaluating ballast fouling levels. Four ballast boxes were constructed with various levels of fouling. GPR testing was conducted using a GSSI (Geophysical Survey Systems, Inc.) device (400, 900, 1600 MHz), and a KRRI (Korea Railroad Research Institute) GPR device (500 MHz), which was developed for ballast tracks. The dielectric permittivity, scattering of the depth (thickness) values, signal strength at the ballast boundary, and area of the frequency spectrum were compared against the fouling level. The results show that as the fouling level increases, the former two variables increase while the latter two decrease. On the basis of these observations, a new integrated parameter, called a ballast condition scoring index (BCSI), is suggested. The BCSI was verified using field data. The results show that the BCSI has a strong correlation with the fouling level of the ballast and can be used as a fouling-level-indicating parameter.

Influence of track irregularities on the vertical acceleration of cars during high-speed traffic

Objective: Obtaining differential equations of the “bridge-train” system, the solution of which allows one to identify the optimal dynamic parameters of the vehicle of high-speed rolling stock and bridge structures when rolling load moves at high speed. Methods: Derivation of differential equations of the “bridge– train” system by the analytical method. Results: Obtaining formulas for determining the acceleration of the spring borne part of rolling stock vehicles depending on track irregularities. Practical importance: Based on the results of calculations according to these formulas, a reasonable assignment of the values of camber and the possibility of assessing the effect of random irregularities of the rail track on the bridge are provided.

A Probabilistic Assessment Model for Train-Bridge Systems: Special Attention on Track Irregularities

In this paper, a probabilistic model devoted to investigating the dynamic behaviors of train-bridge systems subjected to random track irregularities is presented, in which a train-ballasted track-bridge coupled model with nonlinear wheel-rail contacts is introduced, and then a new approach for simulating a random field of track irregularities is developed; moreover, the probability density evolution method is used to describe the probability transmission from excitation inputs to response outputs; finally, extended analysis from three aspects, that is, stochastic analysis, reliability analysis, and correlation analysis, are conducted on the evaluation and application of the proposed model. Besides, compared to the Monte Carlo method, the high efficiency and the accuracy of this proposed model are validated. Numerical studies show that the ergodic properties of track irregularities on spectra, amplitudes, wavelengths, and phases should be taken into account in stochastic analysis of train-bridge interactions. Since the main contributive factors concerning different dynamic indices are rather different, different failure modes possess no obvious or only weak correlations from the probabilistic perspective, and the first-order reliability theory is suitable in achieving the system reliability.

A Novel Snake-Like Model to Simulate Infinite Track for Vehicle–Track Coupling Vibration

The dynamic interaction between the vehicle and track is one of the most critical issues for railways, as it is closely related to running safety. Previously, many vehicle–track coupling models have been developed to study the vibration response of the system. Even though the track is periodic and infinitely extended, only a finite length of the track has often been used in the simulation, so as to reduce the effort of computation. For some special issues, it is necessary to consider the influence of long-wavelength track irregularities on the vehicle responses, and the characteristic track length can reach up to the scale of kilometer. In practice, the computational effort of using a model to accommodate kilometer-long tracks is costly and even unacceptable. To overcome this problem, this paper proposes a novel snake-like model inspired by the famous game Snake to simulate infinite tracks. In the snake-like model, each vehicle can travel on the track repeatedly via the transfer nodes installed at the end of the track. Two examples were presented to verify the accuracy and efficiency of the model proposed. The results showed that the accuracy of snake-like model is consistent with that of existing methods, but the computational effort has been reduced significantly.